1. Field of the Invention
This invention relates to stripping compositions especially useful for photoresist stripping of solid-state integrated circuit components from a substrate, and more particularly, a stripping composition that prevents redeposit of alkali metal ions onto the substrate.
2. Description of the Prior Art
The manufacture of solid-state integrated circuits comprises process steps which include coating onto the surfaces of wafer substrates such as metals, dielectrics and organic polymeric materials to protect areas in the wafer surface that define circuitry patterns. Later in the process it becomes necessary to remove these materials. Numerous compositions have been developed for stripping these organic photoresist polymers from silicon dioxide or other insulator surfaces. The photoresist strippers generally used include compositions comprising mixtures of organic sulfonic acid, phenol and chlorinated hydrocarbon solvents.
A further description of these stripping compositions is found in U.S. Pat. No. 4,165,295, which is incorporated herein by reference. However, the compositions described therein pose grave health and environmental problems. The toxicity and pollution problems arising from the use and disposal of phenol, phenolic derivatives and chlorinated hydrocarbon compounds makes it desirable to provide a suitable replacement.
Phenol-free and chlorinated hydrocarbon-free stripping compositions are described in U.S. Pat. Nos. 4,770,713 and 4,992,108, both to Ward, which are incorporated herein by reference. These compositions provide a non-aqueous biodegradable photoresist stripping combination that can be rinsed with deionized water. Additional biodegradable solvents may also be added.
U.S. Pat. No. 4,636,441 to Sirinyan, et al, which is herein incorporated by reference, discloses the use of crown ether complexes with noble metals in an activation solution to enhance the adhesion strengths of metals deposited on the printed circuit boards. This patented process involves a pretreatment of the substrate board with the crown ether complex before electroless metallization. No specific stripping compositions are disclosed.
A key problem with the use of current stripper compositions is the redeposition of alkali metal ions on the surface of the insulator substrate, such as SiO.sub.2, TEOS, BPSG, etc. In amounts as small as 5 parts per billion, the alkali ion interferes with the electrical properties and deposition of conductor metals at the metal-dielectric interface. This is troublesome in the manufacture of high density integrated circuits, such as, sub-micron connect lead geometrics patterned over dielectrics or "VIA" metal-2 properties connecting with metal-1 over a dielectric "VIA"-hole.
Consequently, while the art of photoresist stripping compositions and methods of stripping are well developed, a need remains for a composition that reduces alkali metal ion concentration on the surface of the dielectric layer of an integrated circuit.